Papers by Author: Antonia Jiménez-Morales

Abstract: This work focuses in the corrosion and wear properties of titanium reinforced with 1% wt. alumina particles, produced by a combination of colloidal techniques and powder metallurgy. The alumina particles were added to control the grain growth of titanium during sintering, and simultaneously to increase hardness and wear resistance. Colloidal techniques permitted a homogeneous dispersion of alumina particles on the surface of fine Ti particles by the formulation of stable aqueous suspensions that were further processed by spray-dry to obtain spherical granules with improved compressibility. Ti-alumina samples were produced by uniaxial pressing of granules and vacuum sintering leading to materials with homogeneous microstructure, a reduction of grain size higher than 50 % with respect to pure titanium, and a sensible increase in hardness. But the addition of ceramic particles can also have an influence on the corrosion behavior that is one of the most interesting properties of titanium alloys, and on wear resistance, that is one of the drawbacks of Ti. Moreover, the study of simultaneous action of wear and corrosion (tribocorrosion) is an area of highest interest in applications like biomedical or automotive. The corrosion behavior was evaluated by Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarization (PP) in NaCl at two concentrations (0.9 % and 3.5 %) and temperatures (37 oC, and room temperature). Tribocorrosion tests were performed using a reciprocating ball-on-plate tribometer where a 10 mm diameter alumina ball was used as counter material, and 10 N normal load was applied during 30 min in the same concentrations and temperatures of NaCl as in the static corrosion tests. The results showed a clear improvement of wear resistance on the composite without reducing the corrosion behavior in both conditions.

Abstract: In this paper we try to summarize the research activities of the PM group in the University Carlos III of Madrid. This research group is highly devoted to PM activities covering different fields (both under the point of view of the materials and the processes). In the PM lab powders can be produced by spray pyrolysis, mechanical alloying and water/gas atomization. These powders can be processed by pressing and sintering, powder injection moulding, isostatic pressing,… Sintering facilities cover vacuum and gas controlled sintering. Regarding the materials, in the group we have different research lines covering low alloyed steels, stainless steels, HSS, ferrites, metal matrix composite (Al and Fe base), Ti, intermetallics, ceramics with functional and structural propierties, … In this paper we describe slightly some of the recent developments produced in the group which is not exhaustive (are there a few more) but representative about we are doing at present.

Abstract: The MIM technology is an alternative process for fabricating near net shape components that usually uses gas atomised powders with small size (< 20 μm) and spherical shape. In this work, the possibility of changing partially or totally spherical powder by an irregular and/or coarse one that is cheaper than the former was investigated. Different bronze 90/10 components were fabricated by mixing three different types of powder: gas atomised spherical powder (usual MIM powder < 22 μm) and two water atomised irregular powders (size < 35 μm and < 140 μm). The blends were made by using only two types of powder in each mixture with the following volume proportions (100/0, 67/33, 33/67, 0/100). The influence of the particle size and shape on the powder packing density and sintering stage was analyzed through the apparent density of the powder blends, as well as, densification, hardness and porosity of the sintered parts. The addition of irregular and/or coarse powder was found to affect the moulding process, although good densifications and hardnesses were obtained in the sintering step. Therefore it could be a promising way to diminish production costs in this technology.

Abstract: In the present work it has been studied the corrosion performance of a powder metallurgical aluminum alloy in aeronautical environments as a function of heat treatment. For this purpose an Al-Cu-Mg prealloyed powder was uniaxially pressed at 600 MPa followed by sintering at 590°C in nitrogen for 60 minutes. Subsequently sintered samples were heat treated to the T4 and T6 state. Corrosion behaviour was assessed by means of potentiodynamic polarization (PPT) in Dilute Harrison solution (DHS), which is considered to closely emulate the atmospheric environment for aircraft. PPT results for the equivalent wrought counterpart, AA2024 in its typical heat treatment for aeronautical applications T3, are also presented for comparison. The microstructure of each sample has been examined by Scanning Electron Microscopy (SEM) and Energy-Dispersive analysis of X-ray (EDX). Similar corrosion performance was observed for both the as sintered sample and its equivalent wrought counterpart, while corrosion resistance of the PM materials was improved by the heat treatment, especially in the T4 state.